Background arts of the technical field include Patent Literature 1. This publication states that “a system for dynamic storage provisioning may comprise: a means for detecting a storage hot-spot located in a first storage pool; and a means for creating a first point-in-time copy of a virtual volume including the storage hot-spot located in the first storage pool in a second storage pool according to the result of the detection.” (Refer to Abstract.) In short, Patent Literature 1 discloses the technology of storing more frequently accessed data in higher-performance devices and storing less frequently accessed data in lower-performance devices.